The present invention relates to a mold for casting a concrete median barrier, and particularly to a mold which can be adjusted to produce selectively different asymmetrical barrier sections conforming to different grade levels of two adjacent roadway lanes.
Modern highway concrete median barriers have a specified profile that has been scientifically developed to receive and contain a travelling vehicle that strikes the barrier, to avoid reflecting the vehicle into adjacent lanes of traffic. As shown in FIGS. 1-3, a barrier 1 of this type has a profile that includes at least one upwardly inward sloping face with two slopes 3, 4, connecting a lower vertical surface 5 and an upper vertical surface 6. The sloping face intersects the lower vertical surface at a level which must be approximately three inches above the surface of an adjacent roadway lane 7 (FIG. 1). Normally, such barriers are symmetrical, having identical profiles on opposite sides, as shown in FIG. 2, resulting in a stable barrier in which the width of the base 9 is several times greater than the width of the top 10. In situations where the roadway lanes 7, 8 on each side of the barrier are at different levels, however, the barrier must be asymmetric with respect to the vertical center plane of the barrier, so that the sloping portions on the two sides commence at the required three inch height above the respective lane surfaces, as shown in FIGS. 1 and 3 where the corresponding portions of the shifted side are identified by the same numerals with a prime. Since the difference in grade between the lanes may vary over the standard 20-foot length of a barrier section, one side profile often must be skewed as well as translated in a vertical plane with respect to the other side profile.
Although it is standard practice to prefabricate standard symmetric median barrier sections under factory controlled conditions, asymmetric barrier sections have had to be cast at the job site in molds specifically set up for each secton. This procedure is expensive and slow; it interferes with other work on the job; and it does not result in the quality of product obtainable at a factory location.
A method and mobile apparatus have been developed (see U.S. Pat. Nos. 3,792,133 and 4,014,633 of Goughnour) for continuously slip casting asymmetrical median barrier walls directly in place on a highway under construction. The apparatus includes a screed having two sidewalls, at least one of the sidewalls being vertically adjustable relative to the other to accommodate variations in grade level of the roadways on the opposite sides of the barrier. This system eliminates the labor needed to set up and take down formwork for successive barrier sections, but the procedure requires close coordination of several different crews preparing the roadbed, setting the reinforcing steel, moving and adjusting the form, and pouring and settling the concrete. The concrete mix used in this process must by "dry" enough to be accurately extruded from the mold but must also be wet enough to be extruded and wet enough to retain entrained air in the mixture (for durability). Such an optimum mixture is difficult to obtain consistently under job site conditions. In addition, the quality of the concrete mix used at a job site cannot be controlled as closely as is possible at a factory site.
Various types of adjustable forms for concrete structures are known, for example for U.S. Pat. Nos. 1,644,587 of Heltzel, 3,071,833 of Tumey, 1,214,870 of Zeiser, 2,610,381 of Rosati et al., 3,704,852 of Wellander, 1,743,965 of Moore, 955,282 of Pocock, and 1,586,352 of Cochran. Each of these prior art mold apparatuses is adapted to solve a specific molding problem, and only the form of Tumey is specifically intended for use in prefabricating a concrete member, as opposed to on-site fabrication. None of them solves the problems involved in providing a reusable, fully adjustable mold for prefabricating asymmetric mediam barriers.